Ascorbic acid (vitamin C) represents an essential nutrient of a proper diet for human beings. To assure the ingestion of this vitamin in sufficient quantities, many individuals regularly supplement their diets with doses of pure vitamin C.
To supply the demand for the vitamin, different processes have proven successful in synthesizing it from other ingredients. Presently, the method disclosed by T. Reichstein, in his U.S. Pat. No. 2,265,121, finds commercial use. That process, however, has only shown itself effective on a starting material of D-glucose or its precursor, corn syrup. A critical stage in the process involves the conversion of 2-keto-L-gulonic acid or derivatives yielding that acid to ascorbic acid. The 2-keto-L-gulonic acid, when treated with acid and warmed to at least 60.degree. C., converts to the ascorbic acid.
However, glucose, the starting material for the Reichstein synthesis represents a generally useful commodity with a market price. Its cost forms a portion of the ultimate charge to the customer.
F. A. Isherwood et al., in their British Pat. No. 763,055, show that .gamma.-lactones of L-gulonic acid or L-galactonic acid may be enzymatically oxidized to ascorbic acid. A group of enzymes which catalyze this reaction appear in seed, animal tissues and many microorganisms. However, the process of Isherwood et al. does not show how to reduce the cost of the initial reactants used to produce the vitamin.
Van Eekelen et al., in U.S. Pat. No. 2,491,065, convert 2-keto-L-gulonic acid to ascorbic acid by heating it in pure water at above 130.degree. C. Bassford, Jr., et al., in their U.S. Pat. No. 2,462,251, use an organic solvent during the rearrangement of the keto-gulonic acid to ascorbic acid. The solvent should lack the ability to form a miscible solution with hydrochloric acid or to dissolve the ascorbic acid. The rearrangement to ascorbic acid takes place under heated conditions with hydrochloric acid which then distills off as an azeotropic mixture with part of the organic solvent. The process produces a slurry of ascorbic acid crystals in the organic solvent. Bassford et al., however, do not suggest how to reduce the cost of the starting reactants required in their reaction.
U.S. Pat. No. 2,702,808 to O. Gisvold oxidizes sorbose with nitrogen tetroxide under anhydrous conditions to provide ascorbic acid. D'Addieco's U.S. Pat. No. 2,847,421 provides an intermediate compound with protected alcohol groups which facilitates the synthesis of ascorbic acid from D-sorbitol. D. F. Hinkley et al., in their U.S. Pat. No. 3,721,663, oxidize a lower alkyl sorboside or fructoside to form glycosidic acids which can then give the corresponding ascorbic acid. The initial reactants for this process take the form of either L-sorbose or D-fructose. Consequently, the effort continues to provide the essential nutrient of vitamin C at lower cost.